VM-3100PRO: ADAT Word Length as it Relates to the VM-3100Pro
ADAT recorders, depending on the model, record only 16-bit audio or both 16-bit
and 20-bit audio. Data carried on the ADAT optical cable is in fact 24-bit
word length; in 16-bit mode (on an ADAT recorder) the eight least significant
bits are filled with zeros, in 20-bit mode the last four bits are zeroes. If
20-bit data is sent to a 16-bit ADAT machine, the four extra bits are simply
ignored. Only ADAT Type II machines (which are the M20, XT20, LX20, and the
ADAT-PCR computer interface card with appropriate software) can receive full
20-bit transfer via the optical cables (and then only if the tapes in those
machines have been formatted in the 20-bit mode).
Some ADAT Type II machines can add dithering. Dither is a specially shaped
mathematical noise added to the bit conversion process which ìsmoothes outî the
transition at low levels and allows better resolution even though the result is
still 16-bit audio.
Since the VM-3100Pro processes 24-bit digital words, no compromise occurs when
connecting to ADAT via the RMDBII. The 24-bit word length of the ADAT digital
audio is retained throughout the signal path from ADAT recorder to VM-3100Pro.